1. Field
The present disclosure relates to photosensitive recording media, and more particularly, to a photopolymer composition for holographic recording, and a holographic recording medium using the photopolymer composition.
2. Description of the Related Art
Upon irradiation by a laser, monomers in a photopolymer composition for holographic recording form a polymer via polymerization. As a result, an interference pattern may be created in the photopolymer composition, and modulation of the refractive index may occur, such that a phase hologram having high diffraction efficiency may be formed.
Unlike silver halide and dichromated gelatin, which have been used as conventional materials for holographic recording, a photopolymer does not have their drawbacks. That is, using a photopolymer for recording holograms does not require a variety of post-processes, including a wet post-process, and enables recording of good quality holograms in real time. The wet post-process means a process wherein a holographic image is developed and fixed by means of a “liquid” developer and a “liquid” fixing agent. For example, the wet post-process may comprises: developing an holographic image by using a liquid developer; removing the liquid developer by means of washing with water; fixing the developed image by using a liquid fixing agent; removing the liquid fixing agent by means of washing with water; dipping the fixed image into a solution of an activating agent; and drying the fixed image.
However, a photopolymer composition may undergo volumetric shrinkage during the conversion of monomers into a polymer. This may result in the tilting of created gratings and a consequential change in diffraction efficiency.
In general, a photopolymer exhibits shrinkage of from about 1% to about 5%. For example, a Bayer MaterialScience's photopolymer has a shrinkage of less than 1.1% (Optics Express, Vol. 19, Issue 27, pp. 26325-26342 (2011)), and a DUPONT photopolymer has shrinkage of from about 3% to 5.5% (SPIE VoL 3005-0277-786X/971). US 2007/0092804 A1 discloses a photopolymer having a low shrinkage of 0.2% obtained via cationic ring-opening polymerization. However, the photopolymer disclosed in US 2007/0092804 A1 requires a high sensitivity of 80 to 100 mJ/cm2.